A common problem for accurate communication is that what is heard in a conversation is often something different than what was said. This proposal investigates three possible causes for this difference. Two factors are characteristic of ordinary language use. These are the expression of meaning and the focus of attention of the listener. The proposed research varies these two in specified ways, and also varies the acoustic stimuli of selected consonants and words in ways that are characteristic of speech perception research. Observed perceptual errors in conversations of children and adults guided the selection. The paradigm is unique in precisely varying acoustic support for perception while determining the influence on what is heard from language context and listeners' beliefs and expectations about the stimuli. The paradigm permits investigation of a) clarity of perception versus accuracy in matching what was said to what was heard, and b) the relative contributions to speech perception of three sources of information which ordinarily coexist in conversation. The general purpose is to explore reasons for verbal misperception and conditions which will enable one to notice and avoid perceptual confusions resulting from hearing something other than what was said.